Basic metals such as calcium, when present in crude oil can lead to fouling of heaters and heat exchangers and poison catalysts used in crude processing. When present as inorganic salts, e.g., chlorides, usually in an oil-encapsulated water phase, the salts can hydrolyze to release corrosive mineral acids. Refinery desalters customarily remove such salts. However, oil-soluble metal salts such as naphthenates and phenolates are not removed by conventional desalting. Therefore, oil-soluble, basic metal-rich crudes are less valuable than crudes with low levels of such metals. A process for metal ion removal enables the increase of the value of such crudes.
A few, but increasingly important, petroleum crude feedstocks, residua, and deasphalted oil derived from them, contain levels of calcium or iron which render them difficult, if not impossible, to process using conventional refining techniques. The metals contaminants causing particular problems are in the form of nonporphyrin, organometallically bound compounds. These species have been attributed to either naturally occurring calcium complexes or solubilized calcium from recovery waters that comes in contact with crude oils. One possible class of calcium compounds identified in particular is the respective naphthenates and their homologous series. These organometallic compounds are not separated from the feedstock by normal desalting processes, and in a conventional refining technique they can cause the very rapid deactivation of hydroprocessing catalysts. Examples of feedstocks demonstrating objectionably high levels of calcium compounds are crudes from China such as Shengli No. 2; DOBA from West Africa; Gryphon and Harding crude oil from the North Sea; and SJV from the West Coast of USA.
Accordingly, there is an ongoing need for the development of new technologies for the effective removal of metal contaminants, particularly calcium, from hydrocarbon feedstocks.